Low-temperature, high-pressure, catalytic, partial conversion of naphtha hydrocarbons to hydrogen



United States Patent LOW-TEMPERATURE, HIGH-PRESSURE, CAT- ALYTIC,PARTIAL CONVERSION OF NAPH- THA HYDROCARBONS T0 HYDROGEN William F.Taylor, Scotch Plains, Francis S. Pramuk, Fanwood, and Barry N.Heimlich, Union, N..l., assignors to Esso Research and EngineeringCompany, a corporation of Delaware No Drawing. Filed Jan. 20, 1964, Ser.No. 338,585 6 Claims. (Cl. 48-214) ABSTRACT OF THE DISCLOSURE Ahydrogen-rich gas product (above 50 mole percent H is produced byreacting paraffinic naphtha hydrocarbons with steam at 550 to 900 F.under a pressure of 150 to 1500 p.s.i.g. in the presence of a catalystcontaining nickel interspersed with silica or alumina, the interspersednickel having a surface area of 20 to 60 m. /g., the reaction beingcontrolled for partial conversion of the hydrocarbons in the range of 5to 40%.

This invention relates to a process for producing hydrogen from normallyliquid hydrocarbons by reaction with steam in the presence of a catalystat relatively low reaction temperatures, high pressures, and high spacevelocities which are controlled for prolonging the activity of thecatalyst in obtaining a partial conversion of the hydrocarbons.

The reaction of normally gaseous hydrocarbons, e.g., methane to butane,with steam in the presence of a catalyst at temperatures above 932' F.(500 C.) to form H with CO or with CO as principal products is known. Itis known that such a reaction goes to completion at above 1000 F., i.e.,at temperatures above the metallurgical limits for usual piping.Although there have been suggestions that such a reaction be carried outunder high pressures, there are difiiculties in supplying the normallygaseous hydrocarbons under elevated pressures and difiiculties of usingapparatus at such high temperatures and pressures. Production of highpressure hydrogen is desirable for a low B.t.u. Town Gas, or for use invarious hydrogenation, hydrogenolysis or hydrocracking processes and inammonia synthesis.

In accordance with the present invention, high pressure hydrogenproduction is obtained at reaction temperatures in the range of 550 F.to 900 F. and mainly below 800 F. with a fresh active catalyst in a veryfast reaction of normally liquid hydrocarbons easily pumped to thedesired reaction pressures, e.g., 5 to 100 atmospheres. The presentinvention is based on a discovery that suitably active catalysts canmake the normally liquid hydrocarbons, particularly those which are C toC paraffins, form mainly H and CO gas products if the residence periodis short enough to limit the formation of methane (CH with a limitedconversion of the feed hydrocarbons.

There are many possible reactions of mixtures containing hydrocarbons, HO, H CO and CO, and the present invention is based on the discovery thatby using a catalyst which makes the reaction of a normally liquidhydrocarbon, e.g., n-hexane, take place quickly at sufliciently lowtemperatures in producing mainly H other undesired reactions such ascracking and carbon formation are minimized. Although this kind ofoperation involves a low or partial conversion of the normally liquidhydrocarbons, the unreacted normally liquid hydrocarbons can beseparated from the gaseous products without substantial lowering ofpressure and with economical lowering of temperature, and then can befed back for reaction.

Another advantage of the low-temperature partial-conversion process isthat it permits the use of highly active 3,395,004 Patented July 30,1968 and nickel-silica catalysts (containing 40 to 60 wt. per-- cent ofNi with 60 to 40 wt. percent of A1 0 or SiO which have high totalsurface areas in the range of to 300 square meters per gram, (mF/g.) andnickel surface areas of 20 to 60 m. g. and these mixed catalysts may bepromoted by certain metals, e.g., Ba, Sr, Cs, Ce, La, Y, Fe, K, and Ca,present as oxides, carbonates, or both oxides and carbonates. Theproportion of promoter may be expressed 0.001 to 1 gram atoms of thepromoter metal per gram atom of Ni.

For obtaining highest H -containing gas products, or highest H /CHratios, with high activity catalysts, the space velocity should be high.The space velocity varies as a function of both the reaction temperatureand pressure to obtain the highest H /CH ratio as brought out in thefollowing examples.

Since highly active catalysts per se and methods for making them areregarded as known in the prior art as exemplified in US. S.N. 317,799,now US. Patent 3,320,- 182, issued May 16, 1967, details on all suchcatalysts are not set forth, but general characterizations andrepresentative examples are given. In general, the highly active nickelcatalysts have the high nickel surface areas mentioned, i.e., above 20mP/g. They are obtained by coprecipitation of nickel with aluminum ashydroxides, carbonates, or basic carbonates from aqueous solutions ofnitrate salts by NH HCO low-temperature (200 to 400 F.) drying of theprecipitates, low temperature (400 to 750 F.) calcining of the driedprecipitates in air, and low-temperature (600 to 750 F.) activation ofthe calcined precipitates by hydrogen. The promoters are admixed asdecomposible compounds, e.g. hydroxides, carbonates, or nitrates withthe precipitates, similarly mixed catalysts of nickel with silica may beprepared using a meta silicate and kieselguhr, in place of aluminumcompounds to have the nickel interspersed with SiO instead of A1 0 Thecatalyst granules may be 1 to 5 mm. particles or compressed largerpellets made from such particles.

The naphtha hydrocarbons used as feed are preheated and mixed withexcess steam to form the reaction mixture at the desirbed temperature.Generally, a ratio of 1.5 to 3 lbs. steam per 1 lb. hydrocarbon is used.

From analyses of products, proportions of reactants, and otherconsiderations, the partial conversion yielding high amounts of hydrogenmay be regarded as involving the following over-all principal reactionpaths, assuming that n-hexane is typical of the average initial normallyliquid hydrocarbon reactant:

Reaction 1 implies that the hydrocarbon initially decomposes in thepresence of steam to liberate hydrogen and form an oxide of carbon,presumedly carbon monoxide. Following this, the carbon monoxidereactions with water to form carbon dioxide and more hydrogen in theso-called Water Gas Shift, or Reaction 2, takes place. The carbonmonoxide may also react with hydrogen to form methane and Water, in theso-called Methanation Reaction (Reaction 3). The thermodynamicequilibrium for Reactions 2 and 3 are known to control the productcomposition at complete hydrocarbon feed conversion. However, Reaction 2is very rapid relative to Reaction 1 since the product contains verylittle carbon monoxide at low conversion levels. Reaction 3 is slowrelative to Reactions 1 and 2. This forms the theoretical basis for thisinvention since it allows a hydrogen-rich product to be formed atprocess conditions, where in terms of equilibrium alone, a hydrogen poorproduct would be expected, i.e., at high pressure and low temperature.This invention, moreover, is based on the unexpected result that ahydrogen-rich product is obtained at low conversion levels, and is notcontingent on the validity of the reaction paths proposed. Reaction 1 isendothermic, and Reaction 2 slightly exothermic. Reaction 3 is stronglyexothermic and tends to increase the temperature in the reaction zone.

EXAMPLE TABLE I Run 1 2 3 4 5 6 Tempcrature,F 600 70 800 900 700 600Pressure, p.s.i.g 350 350 350 500 150 1,000 SpaceVelocity,w.!hr./\v....94 94 5.6 17 25 Percent Hexane Conversion 5 45 19 12 6 Dry Gas ProductComposition (mole percent):

The representative data in the table shows that very high spacevelocities (94 lbs. of hydrocarbon feed per hour per lb. of catalyst)can :be used effectively at temperatures well below 900 F. to produce Has the main conversion product and thus attain the objects of theinvention, i.e., particularly selective high yields of H at highpressure and low temperature.

The experimental data demonstrated that the conversion to H (Reaction 1)and reaction of CO to form CO (Reaction 2) were very rapid sothat thereaction of CO with H to form CH was suppressed.

A comparison of Run 3 with Run 4 shows the need of increasing the spacevelocity and lowering the conversion to obtain the H -rich gas product.

Although the partial conversion to obtain principally H is desired forindustrial use of the H the low B.t.u. product may be used as a fuel gasin areas where a low 300 to 700 B.t.u./s.c.f. Town Gas is desired withthe advantages of low reaction temperatures and high pressures.

Additional experiments have shown that as the reaction temperature isincreased, the pressure should be increased to lower carbon depositionand that as the reaction temperature is increased the catalyst becomesdeactivated more rapidly by thermal and oxidative sintering.Accordingly, for the catalyst to be used economically it should becapable of lasting over 500 hours and this is best obtained attemperatures in the range of 550 F. to 800 F. and pressures of 150 to1500 p.s.i.g., and space velocities of 20 to 100 w./hr./w. or a contacttime of about 36 to 180 seconds. As the catalyst becomes deactivated,with loss of surface area, the reaction temperature can he stepped upe.g., about 5 per 50 hours, and an adequate reaction rate is maintainedas the temperature approaches 900 F.

The high space velocity or short residence period simplifies the controlof temperature in the reaction zone. The reaction products are at a lowtemperature like that of the feed, which means economy of heating andprod- 4' uct separation, in removal of unreacted condensible hydrocarbonreactants, water vapor and of CO by condensation, adsorption, orabsorption.

If the CH content of the gas product is too high, methods can be usedfor removal of the methane such as oxidation. For uses such as hydrogenfor hydrogenolysis or hydrocracking,- some methane can be tolerated inthe hydrogen feed gas.

In cooling the gaseous products, conventional heat exchange means can beused for transferring the heat for preheating water and/or feedhydrocarbons.

In the operation of the partial conversion process under the suitablepressures, the gaseous efliuent from the catalytic reaction zone has alow temperature similar to the inlet temperature and may even be lower,e.g., in the range of 550 to 800 F. with 5 to 40% conversion of lightnaphtha hydrocarbons which are mainly C to C parafi'ins to obtain a gasproduct of above 50 mole percent H with less CO and CH and a slightamount of CO and of other normally gaseous hydrocarbons on a dry basisin addition to H 0 vapor and unconverted naphtha hydrocarbons.

The light naphtha feed is preferably low in sulfur, e.g., below 3 ppm.to minimize the poisoning effect by sulfurcontaining compounds.

The partial conversion for obtaining a gas product of high H /CI-l ratiodiffers from the conversion for obtaining a high heating value fuel gasof high CH /H ratio in several significant ways. The partial conversionfor high I-I/CH ratio is preferably at less than 40% conversion of thenaphtha hydrocarbons, which can occur at lower reaction temperatures,e.g., below 700 F., with a relatively small temperature variation frominlet to outlet of the catalyst bed, e.g., a drop of less than 40 F. Inproducing methane-rich fuel gas, the conversion is preferably above thereaction temperatures are mainly above 700 F., and the temperaturevariation from inlet to outlet of the bed tends to rise more than F. dueto the exothermic methanation reaction.

For the low temperature partial-conversion of the naphtha hydrocarbons,to produce principally hydrogen, there are substantial differences inthe activities of the catalysts of the class called high activitycatalysts. The nickel-Si0 or Ni-kieselguhr catalyst described in theexample is far surpassed in activity for the dehydrogenation/oxidationdecomposition reaction by Ni-Al O catalysts prepared by thecoprecipitation technique with added promoters as shown in the followingTable H:

TABLE II Principal reaction: CuH14+9.6H20- 13H2+6CO+3.6H20

Relative rates of Catalyst: hexane decomposition Ni-kie selguhr 1 Ni-AlO -K 1.8 Ni-Al O -3% Ba 2.5 Ni-Al O -6% Ba 3.5+

The relative hexane decomposition rates can be obtained by determiningthe percent conversion of hexane with the various catalysts undercomparative reaction conditions of temperature, space velocity, andpressure using the same kind of feed.

In an economical use of the process of partial conversion the feed ofnaphtha hydrocarbon mixed with steam are contacted with the catalyst inthe reaction zone during a long run, mainly at temperatures in the rangeof 550 to 800 F. with the catalyst maintained at high activity and thegaseous reaction product of mostly H with lesser amounts of CO CH and COis withdrawn with unreacted naphtha hydrocarbons and steam from thereaction zone to a high pressure condensation zone for separation of thenaphtha hydrocarbons as liquid and con densation of the steam.

The gaseous products with steam and vapors of unreacted naphthahydrocarbons can be made to transfer a substantial amount of heat byheat exchange to water and naphtha feed, then be cooled further forcondensing out the steam and vapors of naphtha hydrocarbons. The gaseousproduct after sufiicient cooling under pressure can be subjected toabsorption treatments for removing CO CO, and CH in order to obtain apurified high pressure hydrogen gas. Absorbing liquids such as aqueoussolutions of alkali carbonates, ethanolamines, glycols, and the likeabsorb CO and moisture. Solid adsorbents such as calcium oxide andsilica gel may be used. Organic solvents, e.g., liquid hydrocarbons,which absorb gaseous hydrocarbon can be used for removing methane. Solidabsonbents, e.g., adsorptive carbon may be used.

The invention described is claimed as follows:

1. Process for producing a gas containing principally H with CO CH andCO which comprises passing a naphtha hydrocarbon feed of principally Cto C paraffin hydrocarbons with steam into contact with a catalystcontaining 40 to 60 wt. percent nickel interspersed with a compoundselected from the group consisting of alumina and silica and havinginitially a nickel surface area of above 20 to 60 square meters per gramand having a total surface area of 100 to 300 m. g. at 550 to 900 F.,under a pressure of 150 to 1500 p.s.i.g., at a space velocity sufiicientto convert 5 to 40% of the hydrocarbon feed to a gas product containingH CO CH and C0 of which H is above 50 mole percent proportion, andrecovering said gas product.

2. Process of claim 1, in which the catalyst contains the 40 to 60 wt.percent Ni with silica.

3. Process of claim 1, in which the catalyst contains to wt. percent Niinterspersed with 60 to 40 wt. percent A1 0 and a promoting metal of thegroup consisting of Ba, Sr, Cs, La, Ce, Y, Fe, K and Ca.

4. Process of claim 1, in which the hydrocarbon feed is contacted withthe catalyst at a space velocity of 20 to lbs. hydrocarbon feed per hourper 1b. of the catalyst.

5. Process of claim 1, in which the gas product is recovered bycondensing out unreacted liquid naphtha hydrocarbons under pressure.

6. Process of claim 1, in Which the naphtha hydrocarbon feed mixed withsteam is contacted with the catalyst of high activity mainly attemperatures in the range of 550 to 800 F. in maintaining the catalystat high activity and the gaseous reaction product is removed withunreacted naphtha hydrocarbons from contact with the catalyst at atemperature in the range of 550 to 800 F. for recovery of the unreactednaphtha hydrocarbons from the gaseous reaction product.

References Cited UNITED STATES PATENTS 3,106,457 10/ 1963 Lockerbie etal. 23-212 3,119,667 1/ 1964 McMahon. 3,162,606 12/1964 Geraitis et al.252-459 X 3,201,214 8/1965 Fox et al 48214 3,271,325 9/1966 Davies eta1. 48-214 X JOSEPH SCOVRONEK, Primary Examiner.

